This invention relates to coated wire and, in particular, to a wire coated with a substantially concentric coating of a normally solid polyarylene sulfide resin composition having improved impact strength and elongation.
Polyarylene sulfide (PAS) resins are attracting attention as high-performance engineering plastics having higher heat resistance, chemical resistance and rigidity than usual engineering plastics such as polycarbonate, polyacetal, nylon and polybutylene terephthalate. Most of these desirable properties are found when PAS is sufficiently crystallized. A relatively recent development has been the use of polyrarylene sulfide compositions such as, for example, polyphenylene sulfide (PPS) compositions, for molding electronic components and as encapsulating materials for electronic components. These compositions typically comprise glass fiber-reinforced polyarylene sulfide. Electronic components are molded or otherwise encapsulated to maintain electrical insulation, to provide mechanical protection and to otherwise shield the metallic components from exposure to the environment.
Polyphenylene sulfide is useful in electronic applications such as in the formation of circuit boards, connectors and the like since polyphenylene sulfide can withstand the temperatures of vapor phase soldering which temperatures often are above 220.degree. without adversely affecting the properties of the molded resin such as blistering or dimensional distortion. Unfortunately, although polyphenylene sulfide has the necessary thermal stability for electronic applications, the material is relatively brittle and, thus, has low impact strength. Moveover, when PPS is crystallized such as by a thermal curing treatment, the elongation thereof is sharply reduced and, thus, the PPS lacks the ability to stretch and is not very tear resistant. Accordingly, PAS is unsuitable for the heat-resistant coating of electric wires to which high elongation is required.
It is known to improve the impact strength of polyarylene sulfide by the addition of elastomeric materials thereto. Thus, U.S. Pat. No. 4,581,411 discloses improving the impact strength of polyarylene sulfide and glass-reinforced polyarylene sulfide by adding from about 0.1 to about 40 wt. % of a polymeric rubber which is selected from among silicon rubber, ethylene-acrylic rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, and poly(butylacrylate) rubber. It is also disclosed that further enhancement of the impact strength of the composition can be achieved when using either the silicon rubber or the poly(butylacrylate) rubber by adding small amounts of an organosilane.
U.S. Pat. No. 4,476,284 discloses polyarylene sulfide compositions which have improved physical properties including impact resistance and flexural modulus by forming the polyarylene sulfide in the presence of a thermoplastic elastomeric hydrogenated conjugated diene/monovinyl arene block polymer. The preferred hydrogenated conjugated diene/monovinyl aromatic block copolymers are isoprene/styrene or butadiene/styrene block copolymers with total average molecular weights on the order of about 25,000-500,000, preferably from about 35,000 to about 300,000. The patent discloses that the desirable effects of the invention are found in the presence of any amount up to and over about 30% of the hydrogenated block copolymer with the preferred range being disclosed as from about 1-5% by weight. While impact strength and the flexural modulus of the PPS resin are improved by the addition of the hydrogenated copolymer, elongation is essentially unchanged or degraded relative to a PPS control without the copolymer.
U.S. Pat. No. 4,451,607 discloses increasing the crystallinity of polyarylene sulfide by blending therewith hydrogenated conjugated diene/monovinyl aromatic block copolymer in an amount up to about 5% by weight. No discussion is rendered relative to the elongation of the blend.
U.S. Pat. No. 4,628,072 discloses improving various properties of many kinds of thermoplastic polymers, including polyarylene sulfide, by addition thereto of partially hydrogenated block copolymers of a monovinyl substituted aromatic hydrocarbon polymer and an olefin polymer block. The block copolymer has grafted thereto a unit containing a carboxylic acid group or derivative thereof. In Table 20 of the patent, blends of PPS and grafted, hydrogenated block copolymer were tested for impact strength, gloss, weatherability and resistance to heat aging relative to PPS blends containing ungrafted and hydrogenated ungrafted block copolymer. Again, no mention is made of the elongation properties of PPS.
None of the above cited patents are directed to specific articles made from polyarylene sulfide or PPS, in particular. In U.S. Pat. No. 4,880,679, there is disclosed an article which provides effective electromagnetic interference (EMI) shielding. In particular, the patent is concerned with an article which comprises electrically conductive fibers embedded in a thermoplastic matrix material. Many thermoplastic matrices are disclosed although polyarylene sulfide including polyphenylene sulfide are among the preferred materials.
U.S. Pat. No. 3,616,186 discloses laminate structures of a polyarylene sulfide coating composition on copper substrates. The patent is specifically concerned with treating a substrate of copper so as to achieve bonding of a polyarylene sulfide resin thereto. The copper metal substrate used in the invention can be in any shape desired including sheeting, wire, coupons, blanks and the like. Coated wire is described as an especially useful application of the laminate structures of the invention. There is no disclosure in the patent of modifying the polyarylene sulfide so as to improve the elongation thereof.
U.S. Pat. No. 4,921,758 discloses improving the elongation of PAS resins and discloses the use of such resins for coating electrical wires. The patent discloses a process of curing a PAS resin to a specified melt viscosity, melt extruding the PAS resin and taking off the extruded PAS resin at a particular taking off speed and finally crystallizing the resin.
Japanese Patent 63-118369 is directed to a polyphenylene sulfide resin composition. The composition comprises 30-99 parts by weight polyphenylene sulfide, 1-70 parts by weight of a polymer produced by grafting an unsaturated carboxylic acid or derivative to a hydrogenated polymer of a conjugated diene or hydrogenated polymer of a conjugated diene and aromatic vinyl hydrocarbon, and 0.1-20 parts by weight of an epoxy resin. It is disclosed that the polyphenylene sulfide composition has improved resilience including improved impact resistance and pliability. The patent states that while PPS is a known high performance engineering plastic having superior heat and chemical resistance, PPS lacks stretchability and tends to be brittle. There is no disclosure on a particular use of the resin composition other than that such compositions are suitable as materials for injection and extrusion molding for use in many areas.